1. Field of the Invention
The present invention relates to a fuel pump, and more particularly to a fuel pump which can be easily balanced and in which there is neither pulsation on the fuel delivered nor production of noise relating thereto.
2. Description of the Prior Art
FIG. 5 is a vertical sectional view showing a conventional Westco type fuel pump placed on the fuel passage of an internal combustion engine wherein a core 4 is fixed on a main shaft 1 functioning as the axis of rotation of an armature of the fuel pump, and a coil 5 is wound around and attached to the core 4. Insulation of the core 4 with respect to the coil 5 is made by applying a powder baking finish to the core 4.
After mounting forcibly the main shaft 1 by sleeves 20A and 20B, the coil 5 is molded by the use of a resin. The sleeves 20A and 20B are disposed so that the main shaft 1 stably supports the coil 5, and further the sleeve 20A is disposed so as to favorably carry the armature in the thrust direction.
A commutator 6 is further mounted on the main shaft 1. The opposite ends of the main shaft 1 are rotatably supported by means of bearings 2 and 3 within a body or casing of the fuel pump.
Reference numerals 7, 8, 21 and 24 designate a brush, a magnet, a washer for a thrust pad of the armature, and a terminal for electric power, respectively.
An impeller 9 is a disk-shaped member having a plurality of grooves 9A defined on the opposite side of the circumferential part thereof. FIG. 7 is a plan view showing the impeller 9. Furthermore, FIG. 6 is an enlarged view showing the impeller 9 and the vicinity thereof in FIG. 5.
One end of the main shaft 1 is machined to define a stepped portion indicated by reference character 1A, and in addition a hole having substantially the same profile as that of said end in its section (a fitting hole having a partially cutout circular profile designated by reference character 9C in FIG. 7) is defined at the central portion of the impeller 9. The stepped portion of the main shaft 1 is inserted into the hole 9C of the impeller 9 so that the impeller 9 is attached and secured to the main shaft 1.
The circumferential portion of the impeller 9 protrudes into a pump chamber 10 shown in FIG. 5.
Meanwhile, when a current is supplied through the terminal 24 to energize the armature of the fuel pump thereby rotating the impeller 9 in a prescribed direction, fuel is sucked through an inlet 13 (in the direction of arrow A). The fuel is passed through the pump chamber 10, internal chambers 11 and 12 of the fuel pump, and discharged from an outlet 14 (along the direction of arrow B).
In order to raise the efficiency of the fuel pump, it is necessary to make a clearance defined by the impeller 9 and each contact face of a pump housing 22 and a pump cover 23 as narrow as possible, and hence it is required to precisely process these contact faces.
In the present example, the impeller 9 is so constructed that the area which must be processed precisely in the surfaces of the impeller 9 is reduced by defining grooves 9B in the area thereof other than each contact area facing against the surfaces of the pump housing 22 or the pump cover 23.
Such a fuel pump as described above has been disclosed, for example, in Japanese Utility Model Laid Open Publication No. 10313/1958.
As mentioned above, in a conventional fuel pump, a stepped portion as indicated by reference character 1A is defined on the one end of the main shaft 1 by means of cutting work, while the fitting hole 9C of a partially cutout circular profile having substantially the same profile in section as that of said end is defined at the central portion of the impeller 9, and the stepped portion 1A of the main shaft 1 is then inserted into the hole 9C of the impeller 9 so that said impeller 9 is mounted on the main shaft 1.
In such construction as described above, however, since the fitting hole 9C defined on the impeller 9 has a partially cutout circular profile, the center of balance in the impeller 9 deviates from the central axis thereof.
Likewise since the stepped portion 1A is defined on the end of the main shaft 1 by cutting the shaft, the center of balance in the main shaft 1 deviates also from the central axis thereof. Accordingly, in a fuel pump involving such a main shaft 1 and impeller 9, it is required to adjust the balance of the armature as a result the fabrication and assembly thereof are troublesome.
Furthermore, the fitting hole 9C of partially cutout circular profile defined on the impeller 9 cannot be worked after molding the impeller 9. Thus, the fitting hole is defined in general at the time of molding the impeller 9. As a result, the central position of the fitting hole 9C cannot be defined with sufficiently high precision. Therefore, it is substantially impossible to make the central axis of the impeller 9 coincident with that of the main shaft 1. In other words, there are many cases where the impeller 9 is eccentrically attached to the main shaft 1. Thus, it is substantially impossible to attain the above-mentioned perfect adjustment in balance.
Consequently, there are instances where pulsation appears in the flow of fuel discharged from the fuel pump or noise is produced.